Hot melt adhesive systems have many applications in manufacturing and packaging. For example, thermoplastic hot melt adhesives are used for carton sealing, case sealing, tray forming, pallet stabilization, nonwoven applications including diaper manufacturing, and many other applications. Hot melt adhesives often come in the form of pellets or particulates and are contained in or provided from an adhesive supply, such as a tank or hopper. The hot melt adhesive pellets are heated and melted by a melter, and liquid hot melt adhesive is pumped to a dispenser, such as a dispensing gun or other applicator which applies the hot melt adhesive to a carton, case, or other objects or substrates. Hot melt adhesive, in its pre-melted state (referred to herein as “particulate” hot melt adhesive), can be provided in a variety of shapes and sizes, ranging from small bb-sized pieces, to larger sized pieces or chips, and still larger “pillows” that are several inches in dimension. Particulate hot melt adhesive must be moved from the adhesive supply to the melter, and the size and shape of the particulate hot melt adhesive and the construction of the adhesive supply and the melter can present challenges that affect this movement.
For example, air-driven, or pneumatic, feed systems use the force of flowing air to move particulate hot melt adhesive from an adhesive supply to a melter. In a known arrangement, a transfer hose connects the adhesive supply with the melter, and an air pump is operated to generate an air flow that moves particulate hot melt adhesive through the transfer hose from the adhesive supply to the melter. However, such pneumatic feed systems have a limit relative to the size of particulate hot melt adhesive they can transfer in a cost effective manner. Larger-dimension particulate hot melt adhesives, including larger pellets, chips, and pillows require a larger-diameter transfer hose than comparatively smaller-sized particulate hot melt adhesives, and also require greater air flow, which can necessitate using a higher performance air pump. In addition, the transfer hose typically connects with a lid on the melter, but heat generated by the melter is transferred to the lid and to adjacent portions of the transfer hose. Transferring heat to the lid and transfer hose can cause premature heating or melting of the hot melt adhesive before it reaches the melter. This can cause problems such as interference with the proper transfer of hot melt adhesive into the melter. Also, air-driven feed systems often include an air filter, which requires periodic replacement or cleaning, and therefore results in system downtime. Furthermore, large bins used as the adhesive supply in air-driven feed systems undesirably increase the overall floor space requirements of the system. In addition, the particulate hot melt adhesives in these large bins can become compacted and begin to stick together, forming larger clumps of particulate hot melt adhesive that are heavier and more difficult to transfer using an air-driven feed system. Further, larger clumps of particulate hot melt adhesive can cause blockages in the transfer hose, which interfere with transferring hot melt adhesive to the melter.
In addition, arrangements have been used where an adhesive supply is positioned directly above the heating elements of a melter, and the force of gravity causes the particulate hot melt adhesive to move downwardly through the adhesive supply to the melter. For example, a hopper can be positioned above the melter, with an outlet of the hopper being connected with an inlet of the melter, so that particulate hot melt adhesive in the hopper falls under its own weight through the outlet of the hopper and directly into the inlet of the melter. Such an arrangement can occupy a smaller footprint on a floor surface than the above-mentioned air-driven feed systems because the adhesive supply is not situated on a floor surface. However, because melters are heated systems, and because the hopper is directly above the melter, heat is transferred from the melter to the hopper, and the hopper becomes heated. Essentially, in such arrangements, the hopper acts as a chimney. Transferring heat to the hopper can cause premature heating or melting of the hot melt adhesive in the hopper, which can interfere with the efficient transfer of hot melt adhesive into the melter.
When feed systems are interrupted from transferring hot melt adhesive from an adhesive supply to a melter, the melter can be starved of new hot melt adhesive and the supply of liquid hot melt adhesive in the hot melt adhesive system can be diminished or completely depleted. This, as well as the other issues discussed above, contributes to downtime of the hot melt adhesive system.
There is a need, therefore, for feed systems for transferring particulate hot melt adhesive from an adhesive supply to a melter that address one or more of the drawbacks discussed above.